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June' 20, 1950 R. H. VARIAN ELEC'ETRICAL CONVERTER Original Filed Oct. 11, 1937 2 SheetsSheet 1 INVENTORl RussuL H. VAR/AN Mr 7 R. H. VARIAN ELECTRICAL CONVERTER June 20, 1950 Original Filed 001;. 11, 1937 2 Sheets-Sheet 2 INVENTOR.

RUSSELL H. VA RIAN g 'ATTORN Y..

Patented June 20, 1950 UNITED STATES OFFICE ELEGTRlCAL Cervantes Russeum Yaria'n, Stanford University, cans, as-

.sign'or to TheBoard of Trustees-or The Leland Stanford Junior University; Stanford University, Calif a corporation of California ina p l c i t t 1. ,i93' ',,,Se' a N 168,355, now Patent No. engazva dated May 20, 1941. Divided and this aiilil cation Maich 2a, 1940, Serial No. 325,634.

This invention relates generallyto ultra high frequency radio apparatus-and method, and the invention has reference more particularly to a novel converter and method forconverting, direct current into ultra high frequency alternating current. This application is a division'of my copending application Serial No. 168 355, filed October ll, 1937, for Electrical converter, now Patent No;,2',242,275,- issued May 20,- 19511.

The principal object ofqthe presentinvention is to provide an efiicient generator or;- thermionic tube means'ior generating ultra highfrequency alternating currents,- said tube meansihavingyall ultra high frequency circuits substantiallyycom fined, thereby eliminating undesired radiation.

Another-object of the present inventionlies in the provision of a novel ultra high frequency oseilIatoremployi-ng a cavity resonator means-together with means forprojectin astream of electrons therethrough for effecting bunchingpf the-electrons of the stream andenergy absorption from: the bunched stream;

Still another object of the-present invention is to provide a method of controlling the flow of electrons in an electron stream which comprises passing the-stream through a region ofstanding eleotromagneticwaves provided in a, hollow resenator to impart variable. velocities. tothe electrons of the streamand then passing the electron stream into an energy absorbing region of electromagnetic waves, energy being conveyed from said energy absorbing region to the-hollow resonator for maintaining the standing waves therein. I

A,;further object of the present invention lies inthe provision of a novel ultra high frequency oscillator having a cavity resonator for effecting velocity modulation of an electron stream and also having a. second cavity resonator suitably spaced from the first sothat the resulting density modulated stream, uponentering the second resonator, serves to set up and maintain'a standing electromagnetic field therein, suitable feed-back means-being providedbetween said second resonator and said first resonator to. maintain oscillations in the latter.

Still another object is: to provide an ultra high frequency oscillator utilizinga minimum starting current.

Yet another object of the present invention is to provide a method and apparatus for controlling the flow of electrons in. an electronstream by passing. the, stream through a region of standing electromagnetic wavesto impartvariable velocities to the: electrons of thestream, and,,;then

17 Claims. (01. 250F215).

passing the electron stream into an energyabsorbingregion of electromagnetic waves, energy beingconveyed from the energy-absorbing region totliegyfirstvregion for maintaining the standing wavestherein. v 1

A still; further. object of thespresent invention is to providea method and apparatus for generatinguultrachigh frequency waves by causing grouping of the electrons of an electron stream, absorbing energy; from these: groups of electrons b13311 electromagnetic field; which may be confinediwithin acavity; resonator, and maintaining grpupsyofrthese:electronsby energy conveyed from; the: energy-absorbiug field to the grouping mea s;

, Stillanotherrobjecttof the present invention is to proyidaarjmethod and; apparatus for generating ultra-high .frequency waves, by passing a stream of-ixelectrons: thruajregion of standing electroma neticw waves; which. may be confined; within a-hollowcavity resonator; and supplying energy from r the "stream; leaving theregion to maintain these standing: waves.

"My, invention possesses numerous other objects and'features of advantage, some of which, to-

-g,ether with-lthe :foregoing, will be set forth in the following description of specific apparatus embodying-,zand utilizing my novel method. It is therefore to be understood that. my method is applicable to other apparatus, and that I do not limit myself, in any way, to the apparatus of the presentapplication, as- I may adopt various other apparatus-embodiments; utilizing the method, within: the scope of the appended claims.

B eferring to the; drawings:

lis a view, partly in longitudinal section andpartlyidiagrammatic, illustrating an oscillator: embodying my invention;

Figozisja fragmentary section of a slight modificationofr the structureshown in Fig. 1;

Fig.3 is aview, partly in section and partly in perspective,-: showing a portion of the resonant circpi-t utilized in thetube shown in Fig. 1;

4- is-, a plan yiew-ofthe toroid space-resonantcirgauit and howitmay be made resilient for; ,tuning purposes; I ;F ig-.. 5 alongitudinal sectional view of an oscillator tube embodying my invention, utilizing .rfes'onatorshaving a relatively large power output and, employing alar e electron stream area.

. Ut i-li'z ing.,.the, principles of the. present invennear. am able to. bui1d oscillating tubes having a high power output at ultra. highfrequencies whichtmay beurepresented by wavelengths, for

..2ani1s1e,,-er. tencentimeters vor less, andv I shall 'electric'resonator 25. are electrically connected and illustrated-with describe a self-oscillator or converter wherein all of the resonant circuits are small enough to be self-contained within a single envelope. In this respect, I employ as a basic,principlegfor the design of the oscillating; circuits, a'confined field resonator, in the form of a hollow metal internall space-resonant or tuned body.

To illustrate my invention, I have showni the drawings a plurality of structures embodying my new method, in order that those skilled in the art may be able, from the disclosure herein, to build other apparatus following the same" broad principles as claimed.

The word grid, as utilized herein, is deemed to refer to any electron-permeable electrode, irrespective of the number of aperturespresent,so

these walls.

- tends between the opposed inner surfaces of the grids 9 and I0. "resonator 25 that coacts with the electron stream placed as to influence electrons or to be influenced by them.

thermionic tube or apparatus connected to control an electron stream, in accordance with my invention, an envelope I is provided atone end thereof with a reentrant stem2' which supports a thermionic cathode 4. It is obvious that any of the known thermionic cathode structures directly or indirectly heated, may be utilized to form'the source of electrons for the tube.

Under the influence of the field between the cathode 4 anda screen or accelerating electrode produced by an accelerating battery 6, the negative terminal of which is connected to the electron-source'cathode 4, the electrons emitted from the cathode '4 are caused to travel therefrom in the form of a stream along a substantially straight-line path. Along this path, the electrons travel through the screen 20, into and through a cavity resonator or space-resonant device 2| i. e., a dielectric resonator consisting of a dielectricfilled space, such as a vacuum or air space, adapted to contain standing electromagnetic waves res'-- onant therein, and having a wave reflecting boundarysurface, of the above described character. The electrons then travel through a space or region 24 and through a second cavity or di- The resonators 2| and 25 their outside surfaces at ground potential, the region 24 being shielded from the fields Within said resonators. I

Two parallel grids 9 and Ill, forming part of the resonator 2|, are disposed in the path of travel of the electron stream. Between these 'grids 9 and ID, the electrons are subjected to the action of an alternating electromagnetic field produced by oscillations within this resonator. After passingthrough the space-resonator 2| and through the space 24, the electronsenter the second space-resonator 25 through an anode grid '21, and travel thereafter through this space-resonator 25 to an anode or plate I2, which may be in the form of a solid wall. If desired the anode I2 may also be permeable as illustrated'in Fig. The electrons after passing through the permeable electrode I2 then may travel to a further anode 56. By reason of the nature of these resonators and their operation, the electromagnetic waves are multiply coherently reflected from the inner walls of the respective resonators. Because "of their construction, shielding between the two erating frequency. 7 v

The resonant alternating electromagnetic fields of these space-resonators, which comprise sus-' The portion of the field of the extends between the opposed inner surfaces of the grid 2'! and the anode I2. Except for the openings through the grids 9, II) and 21, these resonators constitute substantially closed and non-radiating containers, and while the openings in the grid structures permit the passage of the electrons, they do not permit the passage of an appreciable amount of electromagnetic radiation. If, desired, the anode I2 may also be permeable, as illustrated in Fig. 2. ,fIhe electrons, after passing through the permeable electrode I2, may travel to a further anode 56. v The cathode structure 4 should be so designed, and the screen 20 so shaped, that the stream of electrons shall be focused'into a collimated beam that-does not spread excessively, notwithstanding that-it is projected a considerable distance. The form of the screen 2!] depends upon the physical configuration of the apparatus. Though it is connectedthrough the frame of the apparatus to the positive terminal of the accelerating battery 6, it does'not'take part in the hereinafterdescribed cyclic operation of the system.

It is des'irable, for the purpose of most efliciently practicing the invention, that the grids 9 and I 0 be spaced to give an electron flight time therebetween substantially equal to or less than a'half-cycle; or substantially an odd number of half-cycles, in accordance with the initial velocity of the entering electrons, and as determined by thefrequency' of the space-resonant device 2|. Each of the resonators '2I and 25 is shown as reentrant, as described in a copending application 'of William W. Hansen with David L. Webster,

Serial No. 220,414, filed July 1938, now Patent No. 2,227,372, issued December 31, 1940, the front reentrant poles being shown at 2'2 and 26, and the rear reentrant poles at 23 and 29. The resonators "have substantially the exterior shape,

roughly, of a toroid, as indicated in Figs. 3 and shown, The grids 9 and Ill are designed so as to offer as little obstruction to the passage of the electron stream as possible and are located at the inner extremities of the poles 22 and 23 of the resonator 2 I, and the grid '21 and the collector "I2 are also located at the inner extremities of the poles 26 and 29 of the resonator 25. The grids 9, II] and 21 serve to confine the resonator standing fields within the respective resonators. The electron stream, therefore, is projected through the pole 22 and the grid 9 before entering the resonator 2|, through the grid I0 and the pole 23 after leaving it, and through the grid 21 and the pole 26 before entering the resonator 25.

Energy may be transferred to or from the electromagnetic field of a resonator of this character by means of inductive loops or capacitive elements in the field, as Well as by means of a stream of electrons. In the oscillator of Fig. 1, the resonators are shown coupled together by a single coupling loop 30 that enters the respective resonators through adjacent coupling; slots 3| therein. The coupling loop.3|l so interconnects the twov resonators thataany oscillation vset; up in oneresonator shall cause an oscillation to; be set upin the other resonator having a definite-phase relation with the first; The space-resonantdevices2| and 25. are thus excited-andunilaterally coupled together by the stream of electrons pro-v iected through their fields. of electrons will:transmit a disturbance'in resonator 2| to resonator 25; but with. increased amplitude in this latter resonator. The beamwill not transmit a disturbance in the. reverse direction, however, and henceis unilateralin. its action. The degree ofrinsertion of ;th is,loop"into the resonators controls the bilateral coupling. This coupling is termedrbilateral because 'it can convey a disturbance, between" the resonators; in either direction. The. loop in this case conveys apart of the energy of oscillationin resonator 25. back-to resonator 2| because the strength of the standing waves in member 25 is stronger than in'member 2|. The portion of the loop remaining outside may constitutecor be coupled toa radiator or load circuit.

It the deviceis to act as a self-excitedoscillator, the oscillatory field must be automatically built up by the action ofthe electron stream to a high level from a very minute transientvalue; such as that supplied by thermalagitation of electrons in the metal of the resonator 2|, resulting in small departuresigfrom uniformity in the velocity or the density of the electron stream. It is essential; if oscillations areto, be built up, that these small departures in density or velocity shall produce more powerful oscillations in the second resonator 25 than those existing in the first resonator 2|, that produced them. In fact, they must be stronger by a sufficientmargin so that more power can be fed back through looptl! to resonator 2| thanwas initially present in resonator 2|. If this condition is fulfilled, such transient field in resonator 2| willact'to slightly speed up the electrons of certain. portions of the electron stream-and somewhatslow down other portions, while the speed oi -theremaini-ng portions of the stream is unchanged. Electrons entering resonator2| when the minute field therein opposes the stream will be decelerated while those that; enterwhen the field aids the flow. of the stream. will be accelerated.- In the space between resonators-2 t and 25the normal speed electrons tend to overtakethe slower electrons while the faster electrons tend .io-over-v take the normal speed electronsyso, thatsligh-t electron grouping or launching results-.. The-electron. groups on. entering resonator 25,act to reinforce. any transient field which may bepresent duev to thermal agitation or other causes, and which is. in such. phase as to absorb energy from the incipient electron groups, whereasany-transient field in a reverse phase will be damped out by delivering itsenergy to; speed up the; entering electron groups. The resonant circuit 251 will therefore automaticall build up oscillations in such. phase as to extract energy fromany" group ofelectrons appearing with the. proper: frequency between the grid 21 andathe anode I21 If a portion ofxthe energy in the-resonant circuit 25 is transferredhy feed-back totheresonantcircuit 2|, as by means of the coupling loop-309,1. in such. phase as-to enhance thev minute oscillations between. the grids 9 and: it originally-postulated, this enhancement. of the oscillations: will p duceyan increasedi degree of electron grouping That is, the beam between the; grid -2'|- and5 the :anode 12. which; in turn, will increase; the oscillations; in 5: the resonator 25. The initial: faint oscillations ,in the resonator 2 will, therefore, become increased, thus still further increasing-"the grouping. This cyclic process may continue to producestronger and stronger oscillations. until, a steady state of oscillationis achieved.= After the oscillator has reachedzthe-stage ofgfull oscillation, the energy of the; grouped electrons is,largely absorbed "by the field; inthe; space between the grid'21 and the anode I2. I

.Sinceathe amount of energy delivered to the resonant element-25 by the bunching caused "by a given;fieldstrengthbetween the grids 9 and I0 is proportional to the; current innthe electron beam, the above conditions for the setting up of oscillations. may be satisfied only if the current'through the device exceeds a certain-value. Thisminimumcurrent that will result-in oscillation; therefore; depends largely-- upon the losses involved inmaintaining the oscillations betweenthe grids: send 11.0 andbetween the grid, 21 andithe: anode l2. For thi's'reason'the apparatus just described will operate on a very small. starting current because of the exceptionally' low-lossesinherent in cavity resonators 2| and 25.

In; anamplifier, thiscoupling loop 383 may; of course, be omitted, unless reed-back is desired.

OneactuaLpreferred construction of the confinectfieldresonators 2 |-and255is-shovvn in Figs. 3.;and; 4. In Fig. 4,.I,have shownradial slots aiiinlthe resonator wallforthe purpose of making-the resonator slightly resilient so that the energy extracting resonator 25- may be tuned to the-velocity;modulatingrresonator 2|, for: ex-, ample, by changing thespacing between the anode. [Bland-the grid 21. This is accomplished within thejtube in one manner by sealing a metal bellows. to the end of the glass envelope |,;as-shown*in' Fig. 1. A'ituni-n-g;v rodt i-is'connected-totheend of this-bellowed?! and may be moved to; exert pressure against anode I2 by micrometer 3;3 bearing; against. stationary bearings 36. The slots ,tfi-inresonator 25may be very narrow, which case they will not radiate appreciableainounts of energy. It is. interesting to notethat in the type of tubedescribed above he 01 1555. exterior connections-n c ssatrr re he connections ofbattery 6' to cathodedand the resonators; and;v all other connections are within the tube: l

It can be shown both experimentally and mathematicall that when the cathode ray beam is completely velocity grouped, the wave contains veryisha-rp; peaks of electron density. This is equivalent to saying that as the stream: passes argiven pointthe-- density variations with time possesses high; pealgsg. so; that the stream contains stronglhar-moniccomponents. Because of this, it. might-be; supposed that the harmonics of the velocity grouped stream would excite the harmomcs'ofr the hollow resonators, and thus produce. a complex wave form. This is not the case, however, because the harmonics of the beams. are. integral: multiples oftherundamental frequency, whereas the harmonics of the: cavity resonators are in general not: integral multiples of er-fundamental tre uency; Hence, if a partieularrharmonicz oft-he hollow resonator corresponds-to avparticular, harmonic: of the grouped stream, it' iseunlikely that any'other. two harmonies "will correspond, so only-a single armon cireqnencr wilL e prod ce s c 7 the resonance in the cavity resonator is very sharp, the device described is capable of generating a very pure sine wave.

In order for the electromagnetic waves in a hollow resonator to produce a maximum effect on the velocity of an electron during its transit therethrough, the electron flight time therethrough should be one half cycle or less, because if the field reverses before the electron gets through, some of the change in velocity will be canceled by the reversed field before the electron leaves the field. If the flight time in the field must for some reason be longer than one half cycle, it should be an odd number of half cycles, and then one half cycle of the field will be effective in changing the velocity of the electrons.

In causing an oscillator of the kind described to operate, it is necessary that the phase of the oscillations in the electron grouping resonator be such as to deliver electron groups in the right phase to enhance the oscillations in the energy absorbing resonator. It is generally easiest to meet this condition by adjusting the accelerating voltage of the electron beam, and thus to change the transit time of the electrons between the electron grouping resonator and the energy absorbing resonator.

The length of the flight time between the electron grouping and the energy absorbing means will depend upon the requirements of any particular installation. This flight time can be made very short if no regard is had for efficiency. The shorter the flight time is made, thestronger .must be the excitation of the electron grouping circuit, because when the electrons have less time to catch up on each other, their velocity differences must be greater if they are to catch up within such short distances. This increased velocity difference introduces a difficulty in extracting the energy from the electron groups, for the fast electrons of a group will have considerably more energy than the slow electrons of the same group, and if the field extracts all the energy from the fast electrons, the slow electrons will be turned back, and will come out of 'the field on the subsequent half cycle withconsiderable energy. If the field extracts all the energy of the slow electrons, the fast ones will leave the energy absorbing means with considerable energy. This condition can be partially corrected for by rephasing the energy absorbing field slightly, but it cannot be completely cured if the flight time is made too short.

The advantage of the embodiment shown in Fig. 1 lies in the compactness of the apparatus, and the smallness of the current required to make it operate.

Figure 5 illustrates an embodiment of the invention which is preferred if large amounts of power are desired. It is necessarily of larger dimensions, but has very much larger power handling capacity.

In the device of Fig. 5, the resonators M and 25 correspond to the resonators 2| and 25 of Fig. 1. As in Fig. 1, resonator 2! is the electron grouping resonator, and resonator 25' is the energy absorbing resonator. In Fig. 1 the surfaces of the resonator are generated by rotation of the dumb-bell cross-section shown about the vertical axis of symmetry of the cross-section, thereby producing a spheroidal shape with pushed in poles which support the grids 9, I and 21.

The surfaces of the resonators of Fig. 5 on the other hand are generated by rotation of the off- 8 set ordouble dumb-bell cross-section shown about a vertical axis of symmetry of the resulting figure, producing a toroidal or annular figure with pushed in annular poles supporting annular grids 9, l0 and 21. The resonator of Fig. 5 may be considered to be generated by rotating the dumbbell cross-section of the resonator of Fig. 1 about an axis outside this cross-section but parallel to the axis of symmetry thereof. The resonant frequency of these resonators will be somewhat lower for a given cross-section of dumb-bell, i. e., on one side of the axis of symmetry, but not greatly so, whereas the area of grids 9, I0 and 21 is enormously increased. Since the power capacity is primarily governed by the area of these grids, this form will have a greatly increased power capacity.

In order to supply an annular beam of electrons to pass through grids 9, l0 and 21, cathode 4 is provided with an annular ring of emitting material 50. The electron beam is directed from emitter 50 through grids 9, ID and 21, and excites the device in the same manner as already described in connection with Fig. 1.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim and desire to secure by'Letters Paten't is:

1. An alternating current generator comprising an annular cavity resonator comprising a toroidal structure consisting of two annular lobes connected by a narrow apertured annular isthmus, means for projecting an annular stream of electrons across said isthmus to set up a standing electromagnetic field within said cavity resonator, and coupling means extending into said cavity resonator.

2. Apparatus for generating high frequency currents comprising an electron emitter, hollow resonator means, means for projecting an electron stream from said emitter through said hollow resonator means to effect cyclic changes in the velocity of the electrons of said electron stream at the frequency of the hollow resonator means, a second hollow resonator means spaced from said first named resonator means in the direction of travel of said stream for absorbing energy of the frequency of said first resonator means from said electron stream and feed-back means coupling said second hollow resonator means to said first hollow resonator means.

3. Apparatus for generating high frequency currents comprising, means arranged to provide two mutually spaced regions and adapted to contain standing electromagnetic waves resonant therein, an electron emitter, means for drawing electrons therefrom through said first-named means for setting up standing electromagnetic waves therein and establishing alternating electric fields in said spaced regions for acting upon the electron stream, said first named means comprising feed-back means for conveying energy from the second of said regions to the first thereof for maintaining the oscillating field in the latter.

4. Apparatus for generating high frequency currents comprising, means having two mutually spaced substantially annular regions and adapted to contain oscillating electric fields.

means for emitting electrons; means for passing electrons from said emitting means in the-form of an annular stream throughsaidtannular regions inlsuccession for setting ,up the oscillating electricfields therein, said-first named means including means for extracting-energy from. the field of'the second of said regions and for" usin part of said energy tomaintainthe oscillating field in the first of said regions. a

A t forengrav sf e ents currents comprising I electron emitter means 2 for producing a stream of electrons of annular crosssection, annular hollow resonator means, means for projecting said electron stream from said emitter through said annular hollow resonator means to effect cyclic changes in velocity of the electrons of said annular stream at the frequency of the said resonator means, a second annular hollow resonator means spaced from said first resonator in the direction of travel of said stream for absorbing energy of the frequency of said first resonator means from said electron stream, and feed-back means coupling said second resonator means to said first annular hollow resonator means.

6. Apparatus for generating high frequency currents comprising, an electron emitter, hollow resonator means, means for drawing electrons in the form of a stream from said emitter through said hollow resonator means to effect periodic variation of the velocity of the electrons of said stream by the oscillating high frequency electromagnetic field transiently present in said resonator means, said periodic variation in velocity of the electrons of said stream resulting in recurrent grouping thereof after leaving said field, and means for supplying energy derived from said grouped electron stream to said hollow resonator means to maintain said hollow resonator means in a steady state of oscillation.

'7. Apparatus for generating high frequency currents comprising, an electron emitter, annular hollow resonator means, means acting between said emitter and said hollow resonator means for projecting an annular electron stream from said emitter through said resonator means to effect periodic variation of the velocity of the electrons of said electron stream by the oscillating high frequency electromagnetic field transiently present in said resonator means, and means for supplying energy derived from said electron stream after varying the velocity thereof to maintain said hollow resonator means in a steady state of oscillation.

8. Apparatus for generating high frequency currents comprising conductive enclosing means having two mutually spaced regions and adapted to contain oscillating electric field portions resonant therewithin, means in said apparatus for producing an annular stream of electrons, means for passing electrons from said producing means through said regions in succession for setting up the oscillating electric field portions therein, said first-named means including feedback means for extracting energy from the field of said second region and for feeding back part of said energy to maintain the oscillating field in the first of said regions.

9. Apparatus for generating high frequency currents comprising a pair of spaced hollow resonators adapted to contain oscillating electric fields, means in said apparatus for producing an annular stream of electrons and for passing said stream through said resonators in succession for interacting with the oscillating electriic ifilds therein; 1 and feedback means coupling said-vsecondihollow.resonator tossaid first hollow resonaton l #10- flltram gh frequency apparatus comprisingy-a pair -of .,spa cedhollow resonators, each resonator. g. }a pair of, electron permeable walls-meansd ning" adrift space between said 1 stars, .eietr' de mean for projecting a; mantras-arms and defining a path [for said electrons through said resonatorsfsaid electron permeable walls and-said drift space, and feed back means coupling said hollow resonators together.

e llrizl pparatus comprising a hollow resonator having a pair of aligned electron, permeablepor tions, means in said apparatus for producing an electron stream, means defining a path for said stream through said resonator and said electron permeable portions, another resonator in said apparatus, and means coupling said resonators together.

12. In a sealed electronic tube having a glass base portion, an adjustable sealed mounting comprising a flexible metal member having a sealed connection to the base portion and an adjusting member extending through and sealed to the flexible member.

13. An adjustable mounting as set forth in claim 12, in which the metal member comprises a tubular metal element surrounding the adjusting member, mounted at one end on the glass base portion and connected at the other end to the adjusting member.

14. In a sealed electronic tube having a glass base portion, an adjustable sealed mounting comprising a flexible metal member having a sealed connection to the base portion, said member including a flexible tubular element, and an elongated adjusting member extending axially through said tubular element and sealed to said element adjacent the outer end thereof.

15. A hollow resonator having a pair of spaced gratings whereby an electron stream may be passed through the resonator for interaction of the electron stream with electromagnetic waves within the resonator, a source of an electron stream having a given average time rate of fiow of electrons past said gratings, the spacing between the two gratings, and the ratio of open to closed area in the gratings being so proportioned as to provide at the said given average time rate of electron flow a predetermined degree of impedance match between the resonator as a source of waves and the grating as a means for controlling the storage of energy in the electron stream.

16. In combination, means for producing and maintaining a beam of moving electrons having a given average time rate of fiow of electrons therein, and an electromagnetic resonator having a spaced pair of electron permeable electrodes arranged to provide passageway for the electron beam through and beyond said resonator, said electron permeable electrodes having a given spacing and being so designed as to the ratio of electron passing area to electron obstructing area as to give a predesigned degree of coupling for energy transfer between the resonator and the electron beam for electromagnetic variations at a predetermined frequency and for the given electrode spacing and average time rate of flow of electrons.

17. A velocity variation type oscillator comprising an enclosing vessel having a flexible wall portion, a cavity resonator fixedly mounted 11 within said vessel and having opposed walls provided with aligned apertures-one of said walls being flexible and opposite said flexible wall portion, an electron gun opposite one of said walls and. in alignment with said apertures, an electrode opposite the other of said walls and in alignment with the aperture therein, and rigid means connecting said flexible wall portion to said flexible wall.

RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the file of this patent:

Number 12 :UNITED STATES PATENTS Name Date Dallenbach Aug. 30, 1938 Dallenbach Aug. 30, 1938 Hollmann Nov. 21, 1939 Llewellyn Feb. 20, 1940 Dallenbach Apr. 30, 1940 Fritz Mar. 4, 1941 Heil Mar. 18, 1941 Varian May 20, 1941 Ryan May 27, 1941 

